1. Field of the Invention
This invention relates to an anti-lock braking system including a wheel brake, a hydraulic control circuit for controlling the supply of a hydraulic braking pressure to the wheel brake, and a control means for determining whether a wheel is likely to be locked, on the basis of the rotational characteristics thereof, and for making operative the hydraulic control circuit when the wheel is about to be locked, so as to reduce the hydraulic braking pressure supplied to the wheel brake.
2. Description of the Prior Art
When a braking operation is carried out while a vehicle provided with a conventional anti-lock braking system runs on a rough road, the braking force applied to the wheel varies due to the variations in the ground-contacting conditions thereof even if the hydraulic braking pressure is constant. Consequently, the suspension of the vehicle is vibrated longitudinally. This causes the vehicle speed to pulsate in some cases. When such a pulsation of the vehicle speed occurs, the control means judges erroneously that there is the possibility that the wheel is locked, even when there is no such a possibility in practice. As a result, the hydraulic control circuit is energized so as to reduce the hydraulic braking pressure, so that the braking distance increases in some cases.